Chapter 23: the Digestion System

Chapter 23: The Digestion System

I. Digestive Processes-Fig. 23.1 Alimentary canal and related Accessory Organs A. Ingestion-Propulsion (peristalsis)-mechanical digestion-Chemical digestion-Absorption & defecation B. Basic Functional Concepts 1. Both mechanical and chemical stimuli 2. Intrinsic and extrinsic controls-nerve and hormones, short and long reflexes. .Fig. 23.4 C. Digestive Organs: Relationships-parietal and visceral peritoneum-mesentery-retroperitoneal organs D. Blood supply: The splanchnic circulation-arteries that branch off the abdominal aorta to the digestive organs and the Hepatic Portal circulation E. Histology of the Alimentary Canal. Fig. 23.6 Mucosa, submucosa, Muscularis Externa and Serosa F. Enteric Nervous System-submucosal nerve plexus and the myenteric nerve plexus-link to the afferent visceral fibers and by sympathetic (inhibits) and parasympathetic branches (enhance secretory activity) of the autonomic nervous system. II. Functional Anatomy - The Alimentary Canal-the food tube. A. Mouth-Saliva salivary glands, teeth, tongue, taste buds,. Ingestion. Teeth-deciduous, and permanent- dental formula , Fig. 23.11 Mastication, deglutition-buccal phase, pharyngeal-esophageal phase B. Pharynx-epiglottis-bolus C. Esophagus-peristalsis-hiatal hernia D. Stomach-cardiac and pyloric sphincters, greater and lesser curvatures, gastric glands, HCl and pepsin, and chime. Mucosal barrier-3 factors. Fig. 23.7 E. Small Intestine-duodenum. (Fig. 23.21 Duodenum), jejunum, ileum, villi with lacteals and capillaries Fig. 23.22 Surface Area Inc. F. Large Intestine-E. coli, appendix, ascending, transverse and descending colon, rectum, anal sphincters. Fig. 23.9 bacterial flora-haustral contractions-irritable bowel syndrome and diverticulitis. Defecation reflex. II. The Accessory Organs A. Salivary glands, parotid, sublingual and submandibular. B. Liver and gallbladder-bile, storage of fat soluble vitamins Histology, role of bile-hepatitis-gallstones C. Pancreas-pancreatic duct brings enzymes to the small intestine-pancreatic juice Regulation Fig. 23.28 III. Physiology-Digestion overview Table 23.2 A. Chemical vs. Mechanical digestion B. Cephalic phase-nerve and hormone signals Phase 1 C. Gastric phase-chemical stimuli, neural and hormonal, stimulate gastric juices Phase 2 D. Intestinal phase-partially digested food enters the small intestine-hormone Phase 3 E. Most digestion and absorption occurs in the small intestine 1. Proteins-proteases, to dipeptides to amino acids-pepsin, trypsin and chymotrypsin etc. 2. Carbohydrates-to simple sugars 3. Lipids to fatty acids and glycerol (aided by bile emulsification) lipases, triglycerides, bile salts and emulsion 4. Nucleic acids to nucleotides. –pancreatic nucleases F. Absorption-small intestine villi, and lacteals fig. 23.33, & 23, 34 Carbohydrate, protein, lipids vitamins and electrolytes and water. Malabsorption-celiac disease 9gluten-sensitive enteropathy) G. Elimination-defecation, reabsorption of water, diarrhea and constipation. IV. Developmental Aspects-three germ layers A. primitive gut-endoderm-stomodeum and oral membrane. Proctodeum to cloacal membrane to anus. Congenital defects, include cleft palate and cleft lip. Also defects in connection between esophagus and trachea. B. Gastroenteritis-irritation of GI tract, contaminated food or spicy food. Ulcers and gall stones and colon cancers.